JP3663887B2 - Control device for electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus, and more particularly to the configuration of its control circuit.
[0002]
[Prior art]
In an electric power steering apparatus for a vehicle, a steering torque generated in a steering shaft by detecting a steering handle is detected, and a motor that generates a steering assist force is driven based on the detection signal. Some are configured to drive a steering mechanism through an attached reduction mechanism.
[0003]
In such an electric power steering apparatus, a motor drive circuit that drives a motor that generates a steering assist force, and a motor drive circuit that is controlled based on a steering torque detection signal and other signals, etc. A control circuit. The motor drive circuit is connected to the battery via a relay having a normally open contact, and is configured such that when the ignition key is detected ON, the relay contact is closed and power is supplied. ing. The relay is interposed for the purpose of protecting the ignition key contact from a large current flowing in the motor driving circuit and for other safety control.
[0004]
In this type of electric power steering apparatus, a motor that generates a steering assist force uses a motor drive circuit in which semiconductor elements are H-bridge connected, and steering detected by a control circuit constituted by a CPU. Steering torque detected by driving the motor by intermittently turning on / off the semiconductor elements of the motor drive circuit by a pulse width modulation signal (PWM signal) having a predetermined time width determined based on the torque. (For example, see Utility Model Registration No. 2506269).
[0005]
Thus, noise is generated when the motor driving circuit is operating to drive the motor by intermittently turning on / off the semiconductor elements. Therefore, in order to remove noise, it is common to incorporate a noise removal circuit in which a large-capacitance capacitor is inserted in parallel to the motor drive circuit (see, for example, Japanese Utility Model Laid-Open No. 6-27433). ).
[0006]
[Problems to be solved by the invention]
In general, a capacitor having a very large capacity is used as a capacitor incorporated in the motor driving circuit in order to enhance the effect of noise removal. However, when a large-capacity capacitor is used, if the ignition key is turned on and the relay contact is closed to set the motor drive circuit to the operating state, the motor drive circuit is inserted in parallel at that moment. In addition, since a large charging current flows through the capacitor, there is a possibility that the relay contact may be welded.
[0007]
In order to prevent welding of the relay contact due to a large charging current, after the ignition key is turned on, the precharge is gradually started with a small current to the capacitor before the relay contact is closed. However, it is not possible to take a long time until the relay contact is closed after the ignition key is turned on. Therefore, the relay contact is closed without being able to charge a new charge, so that it has not been possible to completely prevent a failure in which a large current flows through the capacitor and the relay contact is welded.
[0008]
It is an object of the present invention to provide a control device for an electric power steering apparatus that solves the above-described problems.
[0009]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the invention according to claim 1 is directed to an electric motor, control means for controlling driving of the electric motor, and motor driving for driving the electric motor. A control device for an electric power steering apparatus that controls driving of the electric motor based on the detected steering torque and applies auxiliary torque to the steering system. An on / off detection circuit for detection; a capacitor connected in parallel to the motor drive circuit; a normally open contact disposed on a power supply circuit for feeding power from the battery to the motor drive circuit; A relay provided with two kinds of normal close contacts arranged on a capacitor charging circuit for charging the capacitor from the battery, and a relay driving circuit for driving the relay, When the ignition key is detected to be off by the on / off detection circuit, the means closes the normal close contact of the relay via the relay driving circuit and sets the charging state of the capacitor. When it is detected that the ignition key is turned on, the normal open contact of the relay is closed via the relay drive circuit to set the motor drive state, and the normal open contact is set. Then, the control device for the electric power steering apparatus is controlled so as to maintain a charged state of the capacitor.
[0010]
The capacitor charging circuit may include a resistance element that sets the charging current to a predetermined value.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. FIG. 1 shows a circuit configuration of a control device. 11 is a CPU, 12 is an ignition key, 13 is a battery, 18 is a constant voltage circuit for supplying a constant voltage to the control system, and 19 is an on / off switch for the ignition key. An on / off detection circuit for detecting a state, 20 is a relay drive circuit, 25 is a relay driven by the relay drive circuit 20, and a normal open contact 25x and a normal close in addition to the common terminal 25a. And a contact point 25y. Reference numeral 21 denotes a motor drive circuit configured by connecting H-bridges of field effect transistors FET1 to FET4, 22 denotes a gate drive circuit for driving the gates of FET1 to FET4, and 23 supplies steering assist force to the steering system. A motor current detecting circuit 24 detects a motor current.
[0012]
The constant voltage circuit 18 supplies a constant voltage Vcc to the CPU 11 and other control systems, and is connected to the positive electrode side of the battery 13 via an ignition key 12.
[0013]
A constant voltage Vcc is supplied to the CPU 11 from a constant voltage circuit 18, and an output of a torque sensor 14 for detecting a steering torque and an output of a steering rotation speed detector 16 are respectively input to the input ports of an A / D converter 15. And 17 are input. A detection signal from the on / off detection circuit 19 for detecting the on / off state of the ignition key 12 and a detection signal from the motor current detection circuit 24 are input to the input port of the CPU 11.
[0014]
A relay drive circuit 20 and a gate drive circuit 22 are connected to the output port of the CPU 11. The relay driving circuit 20 is driven based on the detection signal of the on / off state of the ignition key 12, and the gate driving circuit 22 is determined based on the result of the logical operation executed by the CPU 11 based on the detected steering torque or the like. Driven.
[0015]
The positive side of the battery 13 is always connected directly to the common terminal 25a of the relay 25, and the normally open contact 25x of the relay 25 is a motor drive circuit 21 composed of field effect transistors FET1 to FET4. The normal close contact 25y is connected to the large-capacity electrolytic capacitor C1 through the diode D1 and the resistor R1, and the charging side terminal of the electrolytic capacitor C1 is connected to the motor drive circuit 21. ing. As will be described later, the resistor R1 is a resistor having a relatively high resistance value, and is set to a charging current that does not drive the motor. The diode D1 is for preventing the current from flowing backward from the electrolytic capacitor C1 to the battery 13 side.
[0016]
The resistor R2 is a resistor for detecting the motor current flowing to the motor through the FET1 to FET4. The potential difference between both ends of the resistor R2 is detected by the motor current detection circuit 24, and the detected motor current value is Input to the CPU 11 and motor current feedback control is performed.
[0017]
Next, the operation of the above configuration will be described. The positive side of the battery 13 is always directly connected to the common terminal 25a of the relay 25. When the ignition key 12 is in the off state, the common terminal 25a and the normal close contact 25y are brought into contact with each other and set in a conductive state, that is, the normal close contact 25y is closed, so that the large capacity The electrolytic capacitor C1 is always charged through the normal close contact 25y of the relay 25 and the resistor R1. The resistor R1 is a resistor having a relatively high resistance value, and is set to a charging current that does not drive the motor. Since the charging current is small, no large current flows through the normal close contact 25y, and there is no possibility of welding.
[0018]
Next, when the ignition key 12 is turned on, the on / off detection circuit 19 detects that the ignition key 12 is turned on, and the detection signal is input to the CPU 11, the CPU 11 sends an operation command signal to the relay drive circuit 20. Is output so that the relay 25 is excited, so that the common terminal 25a of the relay 25 and the normally open contact 25x come into contact with each other, that is, the normally open contact 25x is closed. And the normal close contact 25y is set to an open state.
[0019]
Thus, the positive side of the battery 13 is connected to the motor drive circuit 21 via the normally open contact 25x, and the large-capacity electrolytic capacitor C1 is also connected to the positive electrode of the battery 13 via the normal open contact 25x. Connected to the side. At this time, since the electrolytic capacitor C1 is in a charged state, no large current flows through the contact point 25x, and there is no possibility of welding.
[0020]
Thereafter, normal motor drive control is performed. That is, the CPU 11 outputs a PWM signal having a predetermined time width corresponding to the steering assist amount determined based on the steering torque detected by the torque sensor 14 and the steering rotation speed detected by the steering rotation number detector 16, and the like. A data rotation direction signal is output to the gate drive circuit 22. The gate drive circuit 22 drives the FET1 to FET4 of the motor drive circuit 21 to rotate the motor 23 to assist steering.
[0021]
【The invention's effect】
As described above, the control device for the electric power steering apparatus according to the present invention includes an on / off detection circuit that detects the on / off state of the ignition key, and a capacitor that is connected in parallel to the motor drive circuit. 2 types of a normally open contact disposed on a power supply circuit for supplying power from the battery to the motor drive circuit, and a normal close contact disposed on a capacitor charging circuit for charging from the battery to the capacitor. And a relay drive circuit for driving the relay. When the on / off detection circuit detects that the ignition key has been turned off, the relay is provided via the relay drive circuit. -Close the normal close contact of-and set the state of charge to the capacitor. When the ignition key is detected to be on, the Relay - Roh - Maruo - Close Pung contact mode - sets the motor driving state, the Roh - Maruo - and is controlled so as to maintain the state of charge to the capacitor via Pung contacts.
[0022]
As a result, a large-capacitance capacitor for noise removal is always charged even when the ignition key is off, and the ignition drive is on and the motor drive circuit is in operation. Even when set to, the charged state of the capacitor is maintained. Since the capacitor is constantly charged with a relatively small current and no large current flows, the ignition key is turned on and the relay contact is closed to set the motor drive circuit to the operating state as in the conventional device. Then, a possibility that a failure such as a large current flows through the electrolytic capacitor and the relay contact welds at that moment can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of a control device according to an embodiment of the present invention.
[Explanation of symbols]
11 CPU
12 Ignition key
13 Battery 14 Torque sensor 16 Steering rotation sensor 18 Constant voltage circuit 19 On / off detection circuit 20 Relay drive circuit 25 Relay
25a terminal 25x normally open contact 25y normal close contact 21 motor drive circuit 22 gate drive circuit 23 motor 24 motor current detection circuit C1 electrolytic capacitor

Claims (2)

An electric motor, control means for controlling the driving of the electric motor, and a motor drive circuit for driving the electric motor, and the electric motor based on the detected steering torque. In the control device for the electric power steering apparatus that controls the driving of the steering system and applies the auxiliary torque to the steering system,
An on / off detection circuit for detecting an on / off state of the ignition key;
A capacitor connected in parallel to the motor drive circuit;
Two types of contacts, a normally open contact disposed on a power supply circuit for supplying power from the battery to the motor drive circuit, and a normal close contact disposed on a capacitor charging circuit for charging from the battery to the capacitor. A relay with contacts,
A relay driving circuit for driving the relay;
When the ignition key is detected to be off by the on / off detection circuit, the control means closes the normal close contact of the relay via the relay driving circuit to determine the charge state of the capacitor. When the ignition key ON is detected, the normal open contact of the relay is closed via the relay drive circuit to set the motor drive state, and the normal open is set. A control device for an electric power steering apparatus, wherein the control is performed so as to maintain a charged state of the capacitor via a contact. 2. The control device for an electric power steering apparatus according to claim 1, wherein the capacitor charging circuit includes a resistance element for setting a charging current to a predetermined value.

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